Could you spy on someone using a microwave oven as a mic?

While too much of our information streams have become infected with endless discussion of the current White House, this week there’s a direct connection to Leon Theremin. So – let’s dive in, shall we?

In case you’ve managed to avoid US news, you might not know that the Counselor to the President of the United States recently speculated to an interviewer that a microwave oven could be used as a spying device, and specifically, as a camera.

The problem is, what these article claims miss some of the actual mechanics of how espionage occur.

Irrespective of any discussion of the usefulness of this observation, some of the fact checking from the tech press has asked the wrong questions. (This really is a CDM story – just bear with me.)

First, can a microwave oven be used as a spying device? Answer: well, do you mean microwave ovens or microwaves? In fact, not only can you use a microwaves to eavesdrop on people, anyone with some basic electronic skills could build the system themselves. A 2005 article from EE Times shows you how (thanks, Jan Klug):

Here, the idea is to use low-power microwaves to “illuminate” an area and amplify sound in that area.

This is literally (and now unintentionally hilariously) in the Design How-To section of the magazine. Apologies to any EE Times readers I’ve just gotten on a watch list. Hey, more time indoors to work on electronics projects, right? No?

Spying with microwaves is actually reasonably easy, because electromagnetic frequencies reflect physical vibrations – they become a carrier for sound. So even without a microphone, EMF signals can under the right circumstances contain the traces of sound waves as amplitude modulation. s

Now, this won’t come as news to anyone who’s a fan of the history of Leon Theremin, because the inventor of the instrument of the same name also pioneered the technique. I’ve actually shown his invention (The Bug) in lectures, because the story is just too good.

And anyone who’s met Theremin history expert Andrey Smirnov has surely heard the story, as he tells it frequently.

EE Times also credits Lev. But let’s just copy-paste from our friends as the United States NSA:

On August 4, 1945, Soviet school children gave a carving of the Great Seal of the United States to U.S. Ambassador Averell Harriman. It hung in the ambassador’s Moscow residential office until 1952 when the State Department discovered that it was ‘bugged.’

The microphone hidden inside was passive and only activated when the Soviets wanted it to be. They shot radio waves from a van parked outside into the ambassador’s office and could then detect the changes of the microphone’s diaphragm inside the resonant cavity. When Soviets turned off the radio waves it was virtually impossible to detect the hidden ‘bug.’ The Soviets were able to eavesdrop on the U.S. ambassador’s conversations for six years.

The key is the resonant cavity. It doesn’t require a power source, and it’s hard to detect, but you still have to plant the device. Using RF signal as in the example above is advantageous because you don’t have to do that. The EE Times story is a great read, because it gives some history into patent applications around the concept – some of them unrelated to sound detection, looking instead to distance. (I’m told the AutoTune algorithm was first developed for seismic exploration, so remember that imaging and sound are connected.)

Proximity mattered, as far as the original bug. The US Embassy at the time was situated on a busy roadway, close to the sidewalk, in the middle of Moscow. (I’ve been to the location.) Receiving the signal must have been stupidly easy. Theremin’s technique also has the advantage of more successfully penetrating walls.

Here’s the problem: the microwave oven isn’t terribly useful. Theoretically, any large EMF source could have the impact of the illuminating beam above. But I think you might have to try this to see if it works effectively. It could be either that the microwave oven when on created enough EMF disturbance to accidentally recreate the conditions in the EE article, thus amplifying sound signal. The obvious problem there is: it’d only work while the microwave was in use, making this a haphazard intelligence gathering device.

Or, alternatively, every time the microwave oven was on, it’d screw up your existing EMF-based espionage. I’ll be honest, I’m not sure – maybe some expert in our readership can speculate.

Either way, this isn’t a desirable device for the job.

Addendum: Steve Hillman notes on Facebook that the statement “there’s no microphone in a microwave” is itself false. The piezo speaker that produces the beeps is also a mic. Now, you’re scoring points only for pedantry here, because you would have to then get signal from that piezo… at which point you’re hacking into an appliance and you might as well just add your own bug (also originally a Leon Theremin invention). But what the whole episode reveals is that a lot of people actually don’t understand basic electronics and old-fashioned analog-style espionage.

And that brings us to the next question:

Could a microwave be used as an imaging device? Here, the likely answer is – possibly, sort of, but here again it wouldn’t be your first choice.

Now, the couple of tech articles I read on this target may have asked too narrow a question. Given recent revelations that camera-equipped computers and smart TVs used the actual in-built cameras as hacking targets, they asked whether microwaves could be hacked in the same way. There, the answer is pretty definitively no, because there aren’t many microwaves with optical cameras facing outward.

But strictly speaking, can you definitively rule out the possibility of using a microwave as an imaging device? Probably not.

First, yes, there are ways of using electromagnetic radiation to produce an image. See the above technique, and think radar: if you can make a sound, you can make a picture, too. The trick is, you might wind up with a precise image of what someone had put in their microwave, at least using whatever conventional approaches I’ve been able to find. If some lumpen picture of last night’s Chinese take-out is your idea of vital surveillance, then you’ll be happy with this solution. But uh… yeah, that’s unlikely.

Of course, if your objective is spying, getting quality data is important.

Conspiracy theorists, that involves DARPA (US defense funding) and New York City, not far from Trump Tower. But… okay, it’s actually not directly applicable to the microwave oven example. But it does prove that there are unique ways of making sensors, which means there are all sorts of unknowns here – and just talking about webcams and the Internet of Things isn’t sufficient.

In other words, while laughing off the question of whether a microwave oven could be used, the respondents were overly focused on the idea of a literal webcam as necessary for producing an image.

That said, back to reality.

The thing is, clever methods of surveillance become less appealing once you have loads of Internet-connected devices with sensors on them and poor security. And that’s to say nothing of the fact that it’s easy to compromise someone’s existing data simply by guessing their password, or waiting for them to make something public that was intended as private, or any other number of techniques.

But I think what’s more interesting than any of this is the fact that spying is all about doing something that the other person doesn’t expect. That’s what made Theremin a genius. He took a technique that was technologically simple and applied it to a new context, in such a way that no one had thought to look.

They didn’t ask the right questions. And they didn’t precisely state the right answer.

And that’s fundamentally what science is about – asking questions, rather than assuming you have the answers already, and being precise in how you state what answers you find.

By that measure, these articles failed, as did I with my initial kneejerk reaction. Thanks to Tessa Lena via Facebook for calling us out on that.

And I’d say culture is often about finding answers from entirely different questions – which is how the person who is the father of the modern electronic musical instrument is also the father of the modern surveillance state. I just hope, frankly, his weird-sounding music outlives all these other institutions.

With that in mind:

Meanwhile, if you want to learn electronics with the help of the NSA (your tax dollars at work, Americans!), here you go:

And… I’m not helping any of us get our DIY electronic instruments across national borders, am I? Sorry. (Maybe just wink knowingly at border crossing people and tell them they shouldn’t ask more questions, or some people higher up will be displeased. Actually, no, maybe definitely don’t do that.)